|Publication number||US5450394 A|
|Application number||US 08/208,325|
|Publication date||12 Sep 1995|
|Filing date||10 Mar 1994|
|Priority date||10 Mar 1994|
|Publication number||08208325, 208325, US 5450394 A, US 5450394A, US-A-5450394, US5450394 A, US5450394A|
|Inventors||John G. Gruber, Asghar E. Methiwalla, Anil Chandan|
|Original Assignee||Northern Telecom Limited|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (12), Non-Patent Citations (2), Referenced by (176), Classifications (10), Legal Events (8)|
|External Links: USPTO, USPTO Assignment, Espacenet|
CDV=Td-most recent minimum Td.
CDV=Ts1-most recent minimum Ts1.
The present invention relates generally to monitoring performance of a telecommunication network. In particular, it is directed to monitoring of the cell delay between two nodes of a telecommunication network, e.g. ATM networks, frame relay networks etc., using measurement cells, test cells or OAM (Operations, Administration, and Maintenance) cells or, in the case of a frame relay network, test or OAM flames.
Telecommunication networks must be properly maintained to ensure that adequate network performance is achieved and that end-user services are supported. Maintenance functions include "performance management" (continuous in-service performance monitoring for proactive warning of performance degradation) and "fault management" (detection and location of network trouble and failure).
Delay monitoring is important in managing performance of ATM networks and the following parameters are used for such purposes because they affect important network management functions.
Cell Transfer Delay (CTD)
Relates to throughput and response time for high speed data services, and is used for:
provisioning congestion and protocol parameters such as window sizes and time-outs;
selecting low delay routes (e.g. to avoid satellite links); and
deploying echo cancellers.
Cell Delay Variation (CDV)
dimensioning AAL-1 buffers for smoothing CBR (continuous bit rate) traffic;
detecting excessive traffic; and
To support performance and fault management functions of VPC/VCC (virtual path connection/virtual channel connection) in ATM networks, OAM cells are defined to carry operation information such as error checks, node identifiers (IDs), fault descriptions, loopback indications, timestamps, etc. OAM cells are identified in the ATM cell header as separate from user cells.
Bellcore Technical Advisory TA-NWT-001248, Issue 1, October 1992, describes on pages 5-12 and 5-13 how Performance Management OAM cells (PM OAM cells), each containing a timestamp, can be used to obtain an estimate of excessive cell transfer delay occurrences at the broadband switching system that receives the timestamp information in the forward report within the forward monitoring cell. It further states that this count can only be made and stored at the connection/segment end point that receives the forward monitoring cell, because at present there is no field in the PM OAM cell that allows backward reporting of excessive cell transfer delay occurrences. Bellcore goes on to state:
If "the clocks of the BSSs are synchronized in absolute time, . . . the one-way delay can be measured directly with a Performance Management OAM cell. However while the frequencies of the BSSs' clocks will be almost perfectly matched in a BISDN network, the absolute time is not expected to be synchronized. In practice, absolute time differences of several seconds are possible.
Whether the clocks are synchronized or not, there is a lower bound on the delays observed at a receiving node. Delays longer than the minimum would be caused by queuing and processing delays. . . . the parameter of interest is how many delay measurements exceed the maximum allowed value, L+Vmax, where L is the lowest observed value (obtained through calibration). . . .
When the timestamp is being used, it is encoded in the PM OAM cell at the originating end. This time stamp will be accurate to within ±1.0 μsec. The terminating end point compares the time stamp to the time shown by its own clock. This comparison needs to be done as soon as OAM processing has begun on the received PM OAM cell, so that the delay measurement includes as little OAM cell processing time as possible. Variation of the delay experienced by the PM OAM cell will provide a good estimate of the delay variation experienced by the user-information cells.
. . One can estimate the lowest value, L, by a calibration procedure in which the delays of the first C PM cells [C may be e.g. 1000] are observed, and the lowest value is recorded. Note that L may be negative, because the clocks of the two nodes are not necessarily synchronized. The amount by which the observed delay measurements exceed L provides an unbiased estimate of the delay variation."
To summarize, Bellcore states that:
"To measure cell delay variation, the following actions have to be performed:
the originating mode must encode time stamps,
the receiving node must calibrate the first C PM cells to calculate L, and
the receiving node must count the number of PM cells with delays greater than L+Vmax."
Monitoring can be performed at different locations in a network and the following are examples:
a) Near-End monitoring which provides performance of a received signal from its origination to its termination. Bit Interleaved Parity (BIP) is used for ATM by forward monitoring OAM cells. The monitoring point is at the received signal termination.
b) Far-End monitoring provides performance of a transmitted signal from its origination to its termination. For ATM, performance at the far-end termination is sent back to the monitoring point in received signal overhead, e.g. backward reporting OAM cells. The monitoring point is at the received signal termination where the overhead is read.
c) Intermediate monitoring is at intermediate locations in a transparent mode such that near- and far-end performance indicators are read but not terminated. This provides performance of the received signal from its origination to the intermediate monitoring point (e.g. by calculating BIP in forward monitoring OAM cells), and performance of a transmitted signal from its origination to its termination (e.g. by reading backward reporting OAM cells at the intermediate monitoring point).
As seen in the above description, the technique described by Bellcore only provides near-end monitoring, and for one parameter only. The present invention provides near-end and/or far-end monitoring of a number of delay parameters of a telecommunication network such as an ATM or frame relay network.
The present invention can therefore support single-ended monitoring, that is to say, it can monitor performance in both directions from one end. The present invention can further support single-ended monitoring from each node so that both nodes can obtain results of their far-end as well as near-end monitoring.
It is therefore an object of the present invention to provide a method of monitoring performance of a telecommunication network such as an ATM or frame relay network.
It is another object of the present invention to provide a method of monitoring delay parameters of a telecommunication network such as an ATM or frame relay network.
It is a further object of the present invention to provide a method of near-end monitoring of delay parameters of a telecommunication network such as an ATM network using measurement cells.
It is yet a further object of the present invention to provide a method of near-end and far-end monitoring of delay parameters of a telecommunication network such as an ATM network using measurement cells.
It is still another object of the present invention to provide a method of near-end and far-end monitoring of delay parameters of a telecommunication network such as an ATM network using measurement cells to support single-ended monitoring.
It is still a further object of the present invention to provide a method of near-end and far-end monitoring of delay parameters of a telecommunication network such as an ATM network using measurement cells to support single-ended monitoring at both ends.
Briefly stated, the present invention is directed to a method of measuring delay parameters between nodes A and B in a telecommunication network, each node having a clock. The method comprises steps of node A sending to node B a measurement containing timestamp value T1 indicating the time the measurement cell is sent according to the clock at node A, and node B, in response to the measurement cell, sending to node A a reporting measurement cell containing timestamp value T3 and a delay difference value Td, wherein Td=T2-T1, and T2 and T3 are respectively the times the measurement cell is received at node B and the reporting measurement cell is sent from node B according to the clock at node B. The method further includes steps of node A receiving the reporting measurement cell at time T4, according to the clock at node A, and obtaining delay parameters using T1, T3, T4 and Td.
For a more complete understanding of the present invention and for further objects and advantages thereof, reference may now be made to the following description, taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a schematic illustration of a basic concept of the present invention;
FIG. 2 is a schematic illustration of the present invention according to another embodiment; and
FIG. 3 shows a PM OAM cell format.
FIG. 1 depicts schematically the basic concept of near-end and far-end performance monitoring of an ATM network at node A. Near-end and far-end monitoring can be performed independently, however, for convenience the figure shows both. According to one embodiment of the present invention, when monitoring of both near- and far-end is performed, single-ended monitoring is possible at node A. In the figure, the following designations are employed:
-T1 is the timestamp value indicating when a measurement cell is sent from A, according to A's clock;
-T2 is the time the measurement cell is received at B, according to B's clock;
T3 is the timestamp value indicating when a reporting measurement cell is sent from B, according to B's clock; and
T4 is the time the reporting measurement cell is received at A, according to A's clock.
It should be noted that the measurement cell and reporting measurement cell described above can be any specialized cells, they can be test cells, or PM OAM cells. OAM cells are defined in ATM standards and are used for in-service monitoring. The test cells, on the other hand, are used for out-of-service measurements. It is to be understood, therefore, that measurement cells, test cells and OAM cells are interchangeably used throughout this application. OAM cells will be described in more detail below with respect to a different embodiment of the present invention. In frame relay networks, on the other hand, test or OAM frames can be used.
Delays can be expressed as follows:
Td=T2-T1=transfer delay+variable delay+TOD error, at B, for A to B direction; and
Ts=T4-T3=transfer delay+variable delay+TOD error, at A, for B to A direction.
In the above equations, the TOD (Time of Day) error is a discrepancy between individual clocks at A and B and equal in value in each direction; it is considered constant during the period of delay test. The transfer delay is system specific and includes propagation and processing delays. Transfer delay is also considered constant in each direction during the period of delay test. The variable delays are not necessarily equal in each direction. A change in Td or Ts is called cell delay variation (CDV). It should be noted that in unidirectional monitoring (single-ended monitoring at one node), the test is initiated at node A when node A sends a forward monitoring cell or frame to node B and node B responds by sending to node A a backward reporting cell or frame. Full test results are available only at node A. In bidirectional monitoring (single-ended monitoring at both nodes), the test is also initiated at node A but node B not only responds to node A but sends its own forward monitoring cell or frame to node A, thus enabling node A to respond to node B. Full test results are available at both nodes A and B. In one embodiment, node B's backward reporting cell or frame doubles up as its own forward monitoring cell or frame. Referring to FIG. 1 again, the algorithmic process of the present invention is explained as follows:
Node A sends to node B a measurement cell with timestamp T1;
Node B receives the measurement cell and calculates T2-T1 to obtain the delay difference information Td in the direction from A to B
Node B sends to node A a reporting measurement cell containing timestamp T3 and delay difference information Td;
Node A receives the reporting measurement cell at T4.
Thus Node A has in its possession values T1, T3, T4 and Td and will be able to obtain various delay parameters using these values.
Delay difference Ts in the direction from B to A is
and therefore Round Trip Delay (RTD) can be determined as the sum of the delay differences
Equation (3) can be rearranged as below:
Equation (4) thus indicates that RTD is the total round trip delay (T4-T1) less (T3-T2) which includes the cell processing delay and other miscellaneous delays of equipment at node B. From RTD, the cell transfer delay (CTD) in one direction can be estimated as
Estimated CTD=RTD/2. (5)
If Time of Day (TOD) distribution among network nodes were accurate, or in other words, if the clocks at the nodes were perfectly synchronized in absolute time, the TOD error in Equations (1) and (2) would be zero. However, in practice, the TOD error can be of the order of a few seconds, so that direct monitoring of one-way transfer delay using timestamps in Equations (1) and (2) is impractical. However, it should be noted that even if the clocks at the nodes are not synchronized, Equations (3) and (4) are always true for RTD measurement because the TOD error in the direction from A to B in equation (1) will cancel out with the TOD error in another direction from B to A in equation (2). The TOD error is expected to be constant during the period of delay test and can therefore be eliminated by subtracting a fixed delay, such as the minimum of all Td=(T2-T1) samples, from each of the individual Td samples to obtain samples of delay variation. A similar subtraction can be performed in the opposite direction. These subtractions also eliminate the unknown minimum system transfer delay in each direction.
Therefore, Td and Ts in equations (1) and (2) can be replaced by:
Estimated CDV=Td-min.(T2-T1), at B, for A to B direction; (5)
Estimated CDV=Ts-min.(T4-T3), at A, for B to A direction. (6)
It should be noted that the cell processing time of node B requires a separate calculation of T3-T2 because node B does not send T2 to node A. In other words, node A has T1, T3, T4 and Td at its disposal. Furthermore, within reasonable limits, T3 and Td can be sent at an arbitrary time from B to A, thereby disguising the true processing time at node B.
Various other delay parameters can be obtained at node A.
Estimated Maximum Cell Transfer Delay (MCTD)
Estimated CTD=RTD/2=(T4-T1)-(T3-T2). Averaging samples of CTD provides the mean one-way delay, but for certain circumstances it is more useful to monitor the maximum CTD. Thus:
Estimated Max. CTD=Max. RTD/2=Max. [(T4-T1)-(T3-T2)]/2 (7)
This is a reasonable estimate of maximum CTD, since physical routing of ATM connections is the same in each direction, that is to say, propagation and nominal processing delays are similar in each direction, although CDV may differ. In equation (7) Max. RTD is the maximum value among RTD samples obtained by equation (3) or (4).
Cell Delay Variation (CDV)
CDV is with respect to a reference delay which is, for example, the first delay sample or calibrated minimum delay sample. However, the present invention uses the most recent minimum delay difference information as the reference for determining CDV because it is simpler in processing (no calibration needed) and operationally more useful due to the fact that all CDV values are now positive. Thus, for each direction, CDV is the delay difference in that direction less the most recent minimum delay difference in that direction. Therefore, in place of equations (5) and (6), CDV can be expressed as follows:
CDV from A to B=Td--most recent minimum Td (8)
CDV from B to A=Ts--most recent minimum Ts. (9)
Excessive Cell Delay Variation
Excessive CDV is an instance where CDV exceeds a maximum limit, with default limits to be determined. The limits should eventually be limited to a small number of values (2 or 3), but should be settable until the most appropriate values are determined. The expected maximum CDV range is of the order of 1 ms for CBR (constant bit rate) traffic but may be more for VBR (variable bit rate) traffic.
Advantages of this single ended monitoring approach of the present invention are:
neither a Time of Day (TOD) clock (i.e., hour, min., sec., etc.), nor TOD coordination among nodes is required. The TOD error among nodes cancels;
the processing time spent at a particular node can be disguised (within reasonable limits) by sending the far-end timestamp and delay difference at an arbitrary time; and
times T1, T2 and T3 don't need to be stored in the equipment at nodes while the delay measurement is underway. They are effectively stored in the test or OAM cells.
In another embodiment, FIG. 2 illustrates the bidirectional monitoring setup wherein the mirror image of FIG. 1 includes unidirectional monitoring in the opposite direction. Thus in FIG. 2, after unidirectional monitoring is initiated at node A, node B sends a measurement cell with timestamp T5 and node A sends a reporting measurement cell with timestamp T7 and value Ts which in this case is (T6-T5). Node B receives the reporting measurement cell at T8. From FIGS. 1 and 2, each node will have full test results at their disposal and can determine delay parameters such as estimated max. CTD and excessive CDV to each direction. Excessive CDV events counted during 15 min. intervals are accumulated directly over 1 day intervals. In yet another embodiment, the reporting measurement cell which node B sends to node A can also be used as the measurement cell in the opposite direction. In this case, T5 and T6 would be T3 and T4 respectively.
While a measurement cell containing a timestamp has thus far been described, different embodiments use test or PM OAM cells which have fields suitable for the purpose of delay monitoring.
The main performance management functions included in the OAM cell format are shown in FIG. 3.
Forward Monitoring Fields
OAM cell sequence number: (1 byte), detects lost/misinserted OAM cells, which affect the validity of performance monitoring results.
Total User-cell Count (TUC): in cells (2 bytes). The running total of user cell payloads over which error checking has been performed. This technique (as opposed to a simple cell block count), enables the number of lost user cells to be determined when OAM cells are lost.
Error Check Code: BIP-16 (2 bytes), for error detection on a block of user cell payloads.
Backward Reporting Fields
Lost or misinserted cell count: based on TUC (2 bytes). The number of received user cells over which the current error check should be performed, is the difference between the current and previous TUC. If the actual count of user cells is lower, cells have been lost; if higher, cells have been misinserted.
Block Error Result: based on BIP-16 error check (1 byte).
Delay Result: (4 bytes). Used to report delay difference information, e.g., Td=T2-T1 in FIG. 1.
Timestamp: (4 bytes), can be used to monitor cell delay variation which relates to congestion, and is useful as a trigger for engineering additional traffic capacity. This field is shared because it is used for both forward monitoring and backward reporting. Currently, there is no explicit backward reporting field specified for far-end delay variation. However, this field could be used for this purpose, and with the use of the delay result field could provide a far-end monitoring of cell delay variation in both directions.
Delay Accuracy Considerations
As seen in FIG. 3, four byte fields in test cells or PM OAM cells can each be coded as an integer number of clock periods with a range of from 0 to 232 -1 periods. Each period represents a 10 ns unit of time; e.g., a delay of 50 μs would appear as 50/0.01=5000 (10 ns) units. Delay is monitored to an accuracy of ±1 μs. Thus a clock frequency of 1 MHz or more can be used; e.g., each period of a 20 MHz clock represents 1/(20*0.01)=5 (10 ns) units. To achieve this accuracy, TOD coordination is not required since, as noted earlier, the TOD error between nodes cancels. However, clocks with sufficient short term stability are required as discussed below.
For CTD, the error in μs due to clock instability is CTDe=106 δ T, where δ is the relative short term clock stability, and in this case T=CTD is the time in sec. of the delay measurement. Assuming a worst case CTD of 1 sec., then to achieve an error CTDe within ±1 μs, δ must be within 10-6, or 1 PPM.
Similarly, for CDV, the error in μs is CDVe=106 δ T. In this case T is the maximum time between the current delay difference and the most recent minimum delay difference. CDV is monitored over 15 min. intervals. Assuming an unlikely worst case T of 15 min. (900 sec.), to achieve an error CDVe within ±1 μs, δ must be within about 10-9, or 0.001 PPM.
The parameters can be readily determined with stable clocks inherent in network elements (NEs) which, for SONET and switching equipment, are slaved to the synchronization network (δ within 10-11). This applies to clocks in public network NEs, as well as clocks in CPEs which would either be loop-timed to public networks, or slaved to private synchronization networks. It is expected that external test set clocks can either have sufficient short term stability, or can be timed externally from a stable synchronization network clock.
Delay Monitoring Implementation Considerations
Out-of-Service Approach: Test cells would be inserted and extracted at test ports. Test cells could be specialized cells with out-of-service test equipment. For delay monitoring, test cells would have a 4 byte timestamp field to carry T1 forward, and the same field could be used to carry T3 backward. In addition, there would be an additional 4 byte field to carry the delay difference Td=(T2-T1) backward. These fields would be similar in principle to the delay monitoring related fields in the PM OAM cell in FIG. 3.
In-Service Approach: This approach would use the PM OAM cell. At present, the optional 4 byte timestamp field in PM OAM cells is defined for monitoring cells (and for monitoring+reporting cells), and can be used to carry T1 forward. At present, this timestamp field is unused for reporting cells, but could be used to carry T3 backward. As in FIG. 3, an additional optional 4 byte "delay result" field could be defined to carry the delay difference Td=(T2-T1) backward.
Ignored or missing user cells have no bearing on the integrity of delay monitoring as long as a sufficiently large number of samples are reported to reliably determine CTD and CDV.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US4247464 *||1 Oct 1979||27 Jan 1981||General Electric Company||Liquid extraction method for recovering aromatic bisimides|
|US4800560 *||13 Mar 1987||24 Jan 1989||Nec Corporation||Synchronization control capable of establishing synchronization without transmission of distance information between control and local earth stations|
|US4961188 *||7 Sep 1989||2 Oct 1990||Bell Communications Research, Inc.||Synchronous frequency encoding technique for clock timing recovery in a broadband network|
|US5130984 *||18 Dec 1990||14 Jul 1992||Bell Communications Research, Inc.||Large fault tolerant packet switch particularly suited for asynchronous transfer mode (ATM) communication|
|US5255291 *||14 Nov 1988||19 Oct 1993||Stratacom, Inc.||Microprocessor based packet isochronous clocking transmission system and method|
|US5260978 *||30 Oct 1992||9 Nov 1993||Bell Communications Research, Inc.||Synchronous residual time stamp for timing recovery in a broadband network|
|US5276677 *||26 Jun 1992||4 Jan 1994||Nec Usa, Inc.||Predictive congestion control of high-speed wide area networks|
|US5313454 *||1 Apr 1992||17 May 1994||Stratacom, Inc.||Congestion control for cell networks|
|US5381404 *||12 Jul 1993||10 Jan 1995||Mita Industrial Co., Ltd.||Packet-switching communication network and method of design|
|JPH04123549A *||Title not available|
|JPH04207435A *||Title not available|
|JPS63271645A *||Title not available|
|1||*||Bellcore Technical Advisory TA NWT 001248, Issue 1, Oct. 1992, Generic Requirements for Operations of Broadband Switching Systems , pp. 5 12 and 5 13.|
|2||Bellcore Technical Advisory TA-NWT-001248, Issue 1, Oct. 1992, "Generic Requirements for Operations of Broadband Switching Systems", pp. 5-12 and 5-13.|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US5521907 *||25 Apr 1995||28 May 1996||Visual Networks, Inc.||Method and apparatus for non-intrusive measurement of round trip delay in communications networks|
|US5566162 *||7 Dec 1995||15 Oct 1996||Northern Telecom Limited||Method of sectionalizing trouble on telecommunication network connections|
|US5612949 *||5 May 1995||18 Mar 1997||Hewlett-Packard Company||Method and apparatus for determining network delays|
|US5638379 *||6 Jun 1995||10 Jun 1997||Symmetricom, Inc.||Encoding system for distribution of synchronization|
|US5668801 *||21 Jul 1995||16 Sep 1997||Alcatel Str Ag||Method for evaluating a number of discriminated digital data units and for estimating the response time|
|US5692030 *||31 May 1995||25 Nov 1997||Mci Communications Corporation||Electronic interface for exchange of trouble administration information in telecommunications|
|US5717858 *||17 Oct 1994||10 Feb 1998||Motorola, Inc.||Method and structure for prioritizing performance monitoring cells in an asynchronous transfer mode (ATM) system|
|US5719863 *||19 Jan 1996||17 Feb 1998||Siemens Aktiengesellschaft||Method and arrangement for fast through-connect of virtual connections in ATM communications systems|
|US5740159 *||23 May 1996||14 Apr 1998||Northern Telecom Limited||Loopback mechanism for frame relay OAM|
|US5757778 *||6 Dec 1996||26 May 1998||Electronics And Telecommunications Research Institute||Apparatus for testing protocols and traffics in broadband integrated services digital networks and the method thereof|
|US5764626 *||17 Nov 1995||9 Jun 1998||Telecommunications Techniques Corporation||Rate-matched cell identification and modification, replacement, or insertion for test and measurement of ATM network virtual connections|
|US5793976 *||1 Apr 1996||11 Aug 1998||Gte Laboratories Incorporated||Method and apparatus for performance monitoring in electronic communications networks|
|US5802082 *||25 Jul 1996||1 Sep 1998||Deutsche Telekom Ag||Method and device for measuring cell propagation time in ATM networks|
|US5812528 *||17 Nov 1995||22 Sep 1998||Telecommunications Techniques Corporation||Measuring round trip time in ATM network virtual connections|
|US5828670 *||6 Jun 1995||27 Oct 1998||Symmetricom, Inc.||Distribution of synchronization in a synchronous optical environment|
|US5867564 *||27 Feb 1996||2 Feb 1999||Lucent Technologies||Time-of-day clock synchronization in commincations networks|
|US5878032 *||7 Nov 1997||2 Mar 1999||Northern Telecom Limited||Delay monitoring of telecommunication networks|
|US5896388 *||10 Jun 1997||20 Apr 1999||Ncr Corporation||Method and apparatus using GPS to reshape isochronous data at the receiving ends of an ATM network|
|US5974103 *||1 Jul 1996||26 Oct 1999||Sun Microsystems, Inc.||Deterministic exchange of data between synchronised systems separated by a distance|
|US6023455 *||10 Sep 1997||8 Feb 2000||Nec Corporation||Loopback cell control system|
|US6049530 *||20 Jun 1997||11 Apr 2000||Telefonaktiebolaget Lm Ericsson||Segment performance monitoring|
|US6052726 *||30 Jun 1997||18 Apr 2000||Mci Communications Corp.||Delay calculation for a frame relay network|
|US6055247 *||15 Jul 1996||25 Apr 2000||Sony Corporation||Data transmission method, data transmission apparatus and data transmission system|
|US6058102 *||6 Nov 1998||2 May 2000||Visual Networks Technologies, Inc.||Method and apparatus for performing service level analysis of communications network performance metrics|
|US6069876 *||13 Feb 1997||30 May 2000||Nortel Networks Corporation||Performance monitoring of an ATM Network|
|US6118759 *||21 Apr 1997||12 Sep 2000||Fujitsu Limited||Network system and frame relay switch|
|US6147998 *||17 Dec 1997||14 Nov 2000||Visual Networks Technologies, Inc.||Method and apparatus for performing in-service quality of service testing|
|US6201793 *||16 Mar 1998||13 Mar 2001||Lucent Technologies||Packet delay estimation in high speed packet switches|
|US6215772 *||26 Nov 1997||10 Apr 2001||International Business Machines Corporation||Dynamic parameter estimation for efficient transport of HPR data on IP|
|US6260070||30 Jun 1998||10 Jul 2001||Dhaval N. Shah||System and method for determining a preferred mirrored service in a network by evaluating a border gateway protocol|
|US6269084 *||5 May 1998||31 Jul 2001||Oki Electric Industry Co., Ltd.||Time delay based solution of a telecommunication route|
|US6292832||20 Oct 1998||18 Sep 2001||Cisco Technology, Inc.||System and method for determining a preferred service in a network|
|US6298381||20 Oct 1998||2 Oct 2001||Cisco Technology, Inc.||System and method for information retrieval regarding services|
|US6381227||21 Jan 1997||30 Apr 2002||Gilat Florida Inc.||Frame relay protocol-based multiplex switching scheme for satellite mesh network|
|US6445681 *||15 Sep 1999||3 Sep 2002||Vocaltec Communications Ltd.||Method for measuring delay parameters in a network|
|US6446121 *||26 May 1998||3 Sep 2002||Cisco Technology, Inc.||System and method for measuring round trip times in a network using a TCP packet|
|US6449290||12 Jun 1998||10 Sep 2002||Telefonaktiebolaget Lm Ericsson (Publ)||Methods and arrangements in a radio communications system|
|US6532274 *||11 Jan 2000||11 Mar 2003||Telefonaktiebolaget Lm Ericsson (Publ)||Synchronization method and arrangement|
|US6625130||8 Feb 2002||23 Sep 2003||Gilat Satellite Networks, Ltd.||Frame relay protocol-based multiplex switching scheme for satellite mesh network|
|US6628636 *||28 Jun 1999||30 Sep 2003||Rockwell Collins||Method and apparatus for managing communication resources using neighbor segregation|
|US6643612||28 Jun 2001||4 Nov 2003||Atrica Ireland Limited||Mechanism and protocol for per connection based service level agreement measurement|
|US6658607 *||23 May 2000||2 Dec 2003||Eci Telecom Ltd.||Method for detecting troubles of transmission in SDH and SONET|
|US6683856 *||9 Oct 1998||27 Jan 2004||Lucent Technologies Inc.||Method and apparatus for measuring network performance and stress analysis|
|US6687752 *||1 Mar 2000||3 Feb 2004||Ezenial Inc.||Dynamic RTP/RTCP timestamp validation|
|US6711137||12 Mar 1999||23 Mar 2004||International Business Machines Corporation||System and method for analyzing and tuning a communications network|
|US6724724||21 Jan 1999||20 Apr 2004||Cisco Technology, Inc.||System and method for resolving an electronic address|
|US6742031||1 Oct 1999||25 May 2004||Mci Communications Corporation||Delay calculation for a frame relay network|
|US6747951 *||20 Sep 1999||8 Jun 2004||Nortel Networks Limited||Method and apparatus for providing efficient management of resources in a multi-protocol over ATM (MPOA)|
|US6769029 *||7 Aug 2000||27 Jul 2004||Nec Corporation||Method of measuring packet network transmission delay and machine-readable recording medium storing a program for implementing the method|
|US6771617||14 May 2003||3 Aug 2004||Gilat Satellite Networks, Ltd.||Frame relay protocol-based multiplex switching scheme for satellite mesh network|
|US6778493||7 Feb 2000||17 Aug 2004||Sharp Laboratories Of America, Inc.||Real-time media content synchronization and transmission in packet network apparatus and method|
|US6781967||29 Aug 2000||24 Aug 2004||Rockwell Collins, Inc.||Scheduling techniques for receiver directed broadcast applications|
|US6791994||19 Apr 2000||14 Sep 2004||Rockwell Collins, Inc.||Method and apparatus for assigning receive slots in a dynamic assignment environment|
|US6795860||5 Apr 1999||21 Sep 2004||Cisco Technology, Inc.||System and method for selecting a service with dynamically changing information|
|US6810022||29 Aug 2000||26 Oct 2004||Rockwell Collins||Full duplex communication slot assignment|
|US6810045 *||25 Feb 1999||26 Oct 2004||Thomson Licensing S.A.||Method and device for processing data packets which have been received or are to be transmitted on a data channel|
|US6819685 *||19 Nov 1999||16 Nov 2004||Alcatel||Method of and system for controlling a frequency via an asynchronous transmission network and mobile telephone network including the system|
|US6868094 *||4 Nov 1999||15 Mar 2005||Cisco Technology, Inc.||Method and apparatus for measuring network data packet delay, jitter and loss|
|US6885641||1 Dec 1999||26 Apr 2005||International Business Machines Corporation||System and method for monitoring performance, analyzing capacity and utilization, and planning capacity for networks and intelligent, network connected processes|
|US6885651||29 Aug 2000||26 Apr 2005||Rockwell Collins||Maintaining an adaptive broadcast channel using both transmitter directed and receiver directed broadcasts|
|US6901051||15 Nov 1999||31 May 2005||Fujitsu Limited||Server-based network performance metrics generation system and method|
|US6925062 *||18 Dec 2000||2 Aug 2005||Nec Corporation||ATM test equipment operable as source and responder for conducting multiple tests|
|US6996064||21 Dec 2000||7 Feb 2006||International Business Machines Corporation||System and method for determining network throughput speed and streaming utilization|
|US7003098 *||17 Dec 2003||21 Feb 2006||At&T Corp.||Method and system for measurement of the delay through a network link bounded by an echo canceller|
|US7023816||13 Dec 2000||4 Apr 2006||Safenet, Inc.||Method and system for time synchronization|
|US7031264 *||12 Jun 2003||18 Apr 2006||Avaya Technology Corp.||Distributed monitoring and analysis system for network traffic|
|US7092410 *||21 Jan 2005||15 Aug 2006||Cisco Technology, Inc.||Method and apparatus for measuring network data packet delay, jitter and loss|
|US7116639||21 Dec 2000||3 Oct 2006||International Business Machines Corporation||System and method for determining network discrete utilization|
|US7123616||27 Jul 2004||17 Oct 2006||Ixia||Determining round-trip time delay|
|US7137937||26 Jul 2004||21 Nov 2006||Ellen Croft||Collapsible resistance exercise device|
|US7185100||15 Jun 2001||27 Feb 2007||Cisco Technology, Inc.||System and method for determining a preferred mirrored service in a network by evaluating a border gateway protocol|
|US7200596||25 Sep 2001||3 Apr 2007||Cisco Technology, Inc.||System and method for information retrieval regarding services|
|US7274714||15 Jan 2001||25 Sep 2007||Nokia Corporation||Emulating of information flow|
|US7310380||28 May 2004||18 Dec 2007||Rockwell Collins, Inc.||Generic transmission parameter configuration|
|US7327686||12 Nov 2003||5 Feb 2008||Ixia||Generating processed traffic|
|US7360244||29 Dec 2005||15 Apr 2008||Graphon Corporation||Method for authenticating a user access request|
|US7362707 *||23 Jul 2001||22 Apr 2008||Acme Packet, Inc.||System and method for determining flow quality statistics for real-time transport protocol data flows|
|US7380273||29 Dec 2005||27 May 2008||Graphon Corporation||Method for authenticating a user access request|
|US7382799||18 May 2004||3 Jun 2008||Rockwell Collins, Inc.||On-demand broadcast protocol|
|US7385999||20 Oct 2003||10 Jun 2008||Rockwell Collins, Inc.||Heuristics for combining inter-channel and intra-channel communications in a wireless communications environment|
|US7397810||14 Jun 2004||8 Jul 2008||Rockwell Collins, Inc.||Artery nodes|
|US7403780||19 Feb 2004||22 Jul 2008||Rockwell Collins, Inc.||Hybrid open/closed loop filtering for link quality estimation|
|US7424737||6 May 2004||9 Sep 2008||Graphon Corporation||Virtual host for protocol transforming traffic traversing between an IP-compliant source and non-IP compliant destination|
|US7457877||8 Mar 2005||25 Nov 2008||Cisco Technology, Inc.||System and method for measuring round trip times in a network using a TCP packet|
|US7536546||28 Aug 2001||19 May 2009||Acme Packet, Inc.||System and method for providing encryption for rerouting of real time multi-media flows|
|US7561559 *||30 Mar 2005||14 Jul 2009||Ixia||Hardware time stamping and processor synchronization|
|US7606171||28 Jul 2005||20 Oct 2009||Rockwell Collins, Inc.||Skeletal node rules for connected dominating set in ad-hoc networks|
|US7643414||10 Feb 2004||5 Jan 2010||Avaya Inc.||WAN keeper efficient bandwidth management|
|US7657643||23 Jan 2007||2 Feb 2010||Cisco Technology, Inc.||System and method for determining a preferred mirrored service in a network by evaluating a border gateway protocol|
|US7668095||21 Dec 2004||23 Feb 2010||At&T Corp.||Traffic management for frame relay switched data service|
|US7668168||30 Dec 2005||23 Feb 2010||At&T Corp.||Frame relay switched data service|
|US7733794 *||16 May 2006||8 Jun 2010||Alcatel Lucent||Performance monitoring of frame transmission in data network OAM protocols|
|US7764679||27 Dec 2006||27 Jul 2010||Acme Packet, Inc.||System and method for determining flow quality statistics for real-time transport protocol data flows|
|US7792083||5 Jul 2006||7 Sep 2010||Cisco Technology, Inc.||Method and apparatus for measuring network data packet delay, jitter and loss|
|US7817673||27 Mar 2008||19 Oct 2010||Zarlink Semiconductor Limited||Clock synchronisation over a packet network|
|US7826372||26 Mar 2004||2 Nov 2010||Rockwell Collins, Inc.||Network routing process for regulating traffic through advantaged and disadvantaged nodes|
|US7826374 *||19 Dec 2005||2 Nov 2010||Trilliant Networks, Inc.||Method and apparatus for efficient transfer of data over a network|
|US7835290 *||14 Aug 2006||16 Nov 2010||Electronics And Telecommunications Research Institute||Method for measuring end-to-end delay in asynchronous packet transfer network, and asynchronous packet transmitter and receiver|
|US7840664||29 Aug 2003||23 Nov 2010||Ixia||Automated characterization of network traffic|
|US7948906 *||15 Mar 2004||24 May 2011||Realnetworks, Inc.||System and method for determining network conditions|
|US8014286||21 Oct 2008||6 Sep 2011||At&T Intellectual Property Ii, L.P.||Frame relay switched data service|
|US8027257||27 Dec 2009||27 Sep 2011||At&T Intellectual Property Ii, L.P.||Traffic management for frame relay switched data service|
|US8068472||1 Sep 2009||29 Nov 2011||Gilat Satellite Networks, Ltd||Multiplex switching scheme for communications network|
|US8072906 *||11 Aug 2003||6 Dec 2011||Intellectual Ventures I Llc||Signal propagation delay routing|
|US8117298||21 Jul 2010||14 Feb 2012||Graphon Corporation||Multi-homed web server|
|US8155026 *||11 Sep 2008||10 Apr 2012||Verizon Patent And Licensing Inc.||Method and system for identifying network paths|
|US8159957||19 Jun 2009||17 Apr 2012||Ixia||Hardware time stamping and synchronized data transmission|
|US8284795||9 Jun 2005||9 Oct 2012||Broadcom Corporation||Differential delay compensation and measurement in bonded systems|
|US8289871 *||25 Dec 2007||16 Oct 2012||Nihon University||Propagation delay time measuring system|
|US8346861||30 Dec 2011||1 Jan 2013||Graphon Corporation||Web server with animation player|
|US8346890||30 Dec 2011||1 Jan 2013||Graphon Corporation||Multi-homed web server with compiled animation server|
|US8356073||30 Dec 2011||15 Jan 2013||Graphon Corporation||Multi-homed web server with animation player and programmable functionality|
|US8359368||30 Dec 2011||22 Jan 2013||Graphon Corporation||Multi-homed web server with animation player|
|US8364754||30 Dec 2011||29 Jan 2013||Graphon Corporation||Multi-homed web server with compiled animation server and programmable functionality|
|US8369225||23 Sep 2009||5 Feb 2013||Ixia||Network testing providing for concurrent real-time ingress and egress viewing of network traffic data|
|US8370453||30 Dec 2011||5 Feb 2013||Graphon Corporation||Modular multi-homed web server with compiled animation server|
|US8370476||30 Dec 2011||5 Feb 2013||Graphon Corporation||Modular multi-homed web server with animation player|
|US8406139 *||2 Nov 2010||26 Mar 2013||Trilliant Networks, Inc.||Method and apparatus for efficient transfer of data over a network|
|US8427958||30 Apr 2010||23 Apr 2013||Brocade Communications Systems, Inc.||Dynamic latency-based rerouting|
|US8559341||8 Nov 2010||15 Oct 2013||Cisco Technology, Inc.||System and method for providing a loop free topology in a network environment|
|US8576388||17 Jan 2012||5 Nov 2013||International Business Machines Corporation||Optical differential delay tester|
|US8670326||31 Mar 2011||11 Mar 2014||Cisco Technology, Inc.||System and method for probing multiple paths in a network environment|
|US8670329||28 Jan 2013||11 Mar 2014||Ixia||Network testing providing for concurrent real-time ingress and egress viewing of network traffic data|
|US8694626||28 Oct 2010||8 Apr 2014||Ixia||Automated characterization of network traffic|
|US8717896||2 Sep 2011||6 May 2014||At&T Intellectual Property Ii, L.P.||Frame relay switched data service|
|US8724517||2 Jun 2011||13 May 2014||Cisco Technology, Inc.||System and method for managing network traffic disruption|
|US8774010||2 Nov 2010||8 Jul 2014||Cisco Technology, Inc.||System and method for providing proactive fault monitoring in a network environment|
|US8830875||15 Jun 2011||9 Sep 2014||Cisco Technology, Inc.||System and method for providing a loop free topology in a network environment|
|US8848563||12 Jun 2012||30 Sep 2014||Calix, Inc.||Systems and methods for measuring frame loss in multipoint networks|
|US8982733||4 Mar 2011||17 Mar 2015||Cisco Technology, Inc.||System and method for managing topology changes in a network environment|
|US8989032||12 Jun 2012||24 Mar 2015||Calix, Inc.||Systems and methods for measuring frame loss in multipoint networks|
|US9154394||28 Sep 2010||6 Oct 2015||Brocade Communications Systems, Inc.||Dynamic latency-based rerouting|
|US9197691||4 Oct 2011||24 Nov 2015||Google Technology Holdings LLC||System and method for latency measurement at each network element participating as an RTP relay in a telecommunication network|
|US20010053130 *||18 Dec 2000||20 Dec 2001||Hironao Tanaka||ATM test equipment operable as source and responder for conducting multiple tests|
|US20020003776 *||30 Apr 2001||10 Jan 2002||Gokhale Dilip S.||Interworking unit for integrating terrestrial ATM switches with broadband satellite networks|
|US20020080726 *||21 Dec 2000||27 Jun 2002||International Business Machines Corporation||System and method for determining network throughput speed and streaming utilization|
|US20020194343 *||14 Nov 2001||19 Dec 2002||Kishan Shenoi||Measurement of time-delay, time-delay-variation, and cell transfer rate in ATM networks|
|US20030016627 *||23 Jul 2001||23 Jan 2003||Melampy Patrick J.||System and method for determining flow quality statistics for real-time transport protocol data flows|
|US20030051130 *||28 Aug 2001||13 Mar 2003||Melampy Patrick J.||System and method for providing encryption for rerouting of real time multi-media flows|
|US20030108033 *||15 Jan 2001||12 Jun 2003||V. Raisanen||Emulating of information flow|
|US20040228473 *||17 Dec 2003||18 Nov 2004||At& T Corporation||Method and system for measurement of the delay through a network link bounded by an echo canceller|
|US20040236866 *||29 Aug 2003||25 Nov 2004||Diego Dugatkin||Automated characterization of network traffic|
|US20040252646 *||12 Jun 2003||16 Dec 2004||Akshay Adhikari||Distributed monitoring and analysis system for network traffic|
|US20040258099 *||4 Mar 2004||23 Dec 2004||Scott Martin Raymond||Clock synchronisation over a packet network|
|US20050099959 *||12 Nov 2003||12 May 2005||Roger Standridge||Generating processed traffic|
|US20050276223 *||1 Jun 2005||15 Dec 2005||Alcatel||Bandwidth optimization in transport of Ethernet frames|
|US20050286424 *||9 Jun 2005||29 Dec 2005||Broadcom Corporation||Differential delay compensation and measurement in bonded systems|
|US20060007863 *||11 Aug 2003||12 Jan 2006||Siamak Naghian||Signal propagation delay routing|
|US20060013145 *||30 Aug 2005||19 Jan 2006||Samson Boodaghians||Loopback capability for Bi-directional multi-protocol label switching traffic engineered trunks|
|US20060239300 *||30 Mar 2005||26 Oct 2006||Clifford Hannel||Hardware time stamping and processor synchronization|
|US20060285501 *||16 May 2006||21 Dec 2006||Gerard Damm||Performance monitoring of frame transmission in data network oam protocols|
|US20070097865 *||14 Aug 2006||3 May 2007||Song Jong T||Method for measuring end-to-end delay in asynchronous packet transfer network, and asynchronous packet transmitter and receiver|
|US20070130355 *||23 Jan 2007||7 Jun 2007||Cisco Technology, Inc.||System and Method for Determining a Preferred Mirrored Service in a Network by Evaluating a Border Gateway Protocol|
|US20070140127 *||19 Dec 2005||21 Jun 2007||Skypilot Network, Inc.||Method and apparatus for efficient transfer of data over a network|
|US20090257354 *||19 Jun 2009||15 Oct 2009||Clifford Hannel||Hardware Time Stamping and Synchronized Data Transmission|
|US20100061264 *||11 Sep 2008||11 Mar 2010||Verizon Business Network Services Inc.||Method and system for identifying network paths|
|US20100128770 *||21 Nov 2008||27 May 2010||Adrian Stanciu||Measuring Delay in a Network Segment and/or through a Network Communications Device|
|US20100195517 *||25 Dec 2007||5 Aug 2010||Nihon University||Propagation delay time measuring system|
|US20100254277 *||27 Nov 2008||7 Oct 2010||Telefonaktiebolaget L M Ericssson (Publ)||Method and Arrangement in a Telecommunication System|
|US20110040874 *||17 Feb 2011||Diego Dugatkin||Automated Characterization of Network Traffic|
|US20110058494 *||2 Nov 2010||10 Mar 2011||Trilliant Networks, Inc.||Method and apparatus for efficient transfer of data over a network|
|US20110069626 *||24 Mar 2011||Ethan Sun||Network testing providing for concurrent real-time ingress and egress viewing of network traffic data|
|US20110170537 *||14 Jul 2011||Marius Ungureanu||One Way and Round Trip Delays Using Telephony In-Band Tones|
|USRE41000 *||3 Sep 2004||24 Nov 2009||Telefonaktiebolaget L M Ericsson (Publ)||Methods and arrangements in a radio communications system|
|CN100550786C||15 Jun 2006||14 Oct 2009||阿尔卡特公司||Performance monitoring of frame transmission in data network OAM protocols|
|CN100593301C||11 Aug 2003||3 Mar 2010||斯比德航海有限公司||Signal propagation delay routing|
|EP0804047A2 *||6 Feb 1997||29 Oct 1997||Deutsche Telekom AG||Method for measuring the switching delay in an ATM network|
|EP0915635A1 *||2 Nov 1998||12 May 1999||Northern Telecom Limited||Delay monitoring of telecommunication networks|
|EP1109360A1 *||15 Dec 2000||20 Jun 2001||Nec Corporation||ATM test equipment operable as source and responder for conducting multiple tests|
|EP1215559A2 *||5 Dec 2001||19 Jun 2002||Chrysalis- ITS Inc.||Method and system for time synchronization|
|EP1608112A1 *||9 Mar 2005||21 Dec 2005||Broadcom Corporation||Differential delay compensation and measurement in bonded systems|
|WO1996034476A1 *||17 Apr 1996||31 Oct 1996||Visual Networks Inc||Method and apparatus for non-intrusive measurement of round trip delay in communications networks|
|WO1997037310A1 *||27 Mar 1997||9 Oct 1997||Gte Laboratories Inc||Performance monitoring of an atm switch|
|WO2001020825A1 *||14 Sep 2000||22 Mar 2001||Vladimir Pogrebinsky||Method for measuring delay parameters in a network|
|WO2009082334A1 *||27 Nov 2008||2 Jul 2009||Ericsson Telefon Ab L M||Method and arrangement in a telecommunication system|
|WO2010118569A1 *||14 Apr 2009||21 Oct 2010||Huawei Technologies Co., Ltd.||Ip network performance measurement method, apparatus and system|
|U.S. Classification||370/253, 375/354|
|International Classification||H04Q11/04, H04L12/56, H04J3/06|
|Cooperative Classification||H04Q11/0478, H04L2012/5649, H04L2012/5628, H04L2012/5652|
|9 Jun 1994||AS||Assignment|
Owner name: BELL-NORTHERN RESEARCH LTD., CANADA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:GRUBER, JOHN GERALD;METHIWALLA, ASGHAR EBRAHIM;CHANDAN, ANIL;REEL/FRAME:007017/0620;SIGNING DATES FROM 19940303 TO 19940304
Owner name: NORTHERN TELECOM LIMITED, CANADA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:BELL-NORTHERN RESEARCH LTD.;REEL/FRAME:007017/0649
Effective date: 19940527
|7 Jan 1999||FPAY||Fee payment|
Year of fee payment: 4
|23 Dec 1999||AS||Assignment|
|30 Aug 2000||AS||Assignment|
Owner name: NORTEL NETWORKS LIMITED,CANADA
Free format text: CHANGE OF NAME;ASSIGNOR:NORTEL NETWORKS CORPORATION;REEL/FRAME:011195/0706
Effective date: 20000830
|24 Feb 2003||FPAY||Fee payment|
Year of fee payment: 8
|28 Mar 2007||REMI||Maintenance fee reminder mailed|
|12 Sep 2007||LAPS||Lapse for failure to pay maintenance fees|
|30 Oct 2007||FP||Expired due to failure to pay maintenance fee|
Effective date: 20070912